ImageSharp/tests/ImageSharp.Tests/Processing/Processors/Transforms/KernelMapTests.cs

using System;
using System.IO;
using System.Text;

using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using SixLabors.ImageSharp.Processing.Processors.Transforms;
using SixLabors.Primitives;

using Xunit;
using Xunit.Abstractions;

namespace SixLabors.ImageSharp.Tests.Processing.Processors.Transforms
{
    public partial class KernelMapTests
    {
        private ITestOutputHelper Output { get; }

        public KernelMapTests(ITestOutputHelper output)
        {
            this.Output = output;
        }

        /// <summary>
        /// resamplerName, srcSize, destSize
        /// </summary>
        public static readonly TheoryData<string, int, int> KernelMapData = new TheoryData<string, int, int>
        {
            { nameof(KnownResamplers.Bicubic), 15, 10 },
            { nameof(KnownResamplers.Bicubic), 10, 15 },
            { nameof(KnownResamplers.Bicubic), 20, 20 },
            { nameof(KnownResamplers.Bicubic), 50, 40 },
            { nameof(KnownResamplers.Bicubic), 40, 50 },
            { nameof(KnownResamplers.Bicubic), 500, 200 },
            { nameof(KnownResamplers.Bicubic), 200, 500 },

            { nameof(KnownResamplers.Lanczos3), 16, 12 },
            { nameof(KnownResamplers.Lanczos3), 12, 16 },
            { nameof(KnownResamplers.Lanczos3), 12, 9 },
            { nameof(KnownResamplers.Lanczos3), 9, 12 },
            { nameof(KnownResamplers.Lanczos3), 6, 8 },
            { nameof(KnownResamplers.Lanczos3), 8, 6 },

            // TODO: What's wrong here:
            // { nameof(KnownResamplers.Lanczos3), 20, 12 },

            {nameof(KnownResamplers.Lanczos8), 500, 200 },
            {nameof(KnownResamplers.Lanczos8), 100, 10 },
            {nameof(KnownResamplers.Lanczos8), 100, 80 },
            {nameof(KnownResamplers.Lanczos8), 10, 100 },
        };

        [Theory]
        [MemberData(nameof(KernelMapData))]
        public void KernelMapContentIsCorrect(string resamplerName, int srcSize, int destSize)
        {
            var resampler = (IResampler)typeof(KnownResamplers).GetProperty(resamplerName).GetValue(null);
            
            var kernelMap = KernelMap.Calculate(resampler, destSize, srcSize, Configuration.Default.MemoryAllocator);

            var referenceMap = ReferenceKernelMap.Calculate(resampler, destSize, srcSize);

#if DEBUG
            string text = PrintKernelMap(kernelMap);
            this.Output.WriteLine(text);
#endif

            for (int i = 0; i < kernelMap.DestinationSize; i++)
            {
                ResizeKernel kernel = kernelMap.GetKernel(i);

                ReferenceKernel referenceKernel = referenceMap.GetKernel(i);

                Assert.Equal(referenceKernel.Length, kernel.Length);
                Assert.Equal(referenceKernel.Left, kernel.Left);
                Assert.True(kernel.GetValues().SequenceEqual(referenceKernel.Values));
            }
        }

        private static string PrintKernelMap(KernelMap kernelMap)
        {
            var bld = new StringBuilder();

            for (int i = 0; i < kernelMap.DestinationSize; i++)
            {
                ResizeKernel kernel = kernelMap.GetKernel(i);
                bld.Append($"({kernel.Left:D3}) || ");
                Span<float> span = kernel.GetValues();

                for (int j = 0; j < kernel.Length; j++)
                {
                    float value = span[j];
                    bld.Append($"{value,8:F5}");
                    bld.Append(" | ");
                }

                bld.AppendLine();
            }

            return bld.ToString();
        }
    }
}